|
A brilliant is a diamond or other gemstone, cut in a particular form with numerous facets so as to have exceptional brilliance. The shape resembles that of a cone and provides maximized light return through the top of the diamond. Even with modern techniques, the cutting and polishing of a diamond crystal always result in a dramatic loss of weight; rarely is it less than 50%. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a ''fancy cut''—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to. ==Facet proportions and names== The original round brilliant-cut was developed by Marcel Tolkowsky in 1919. The modern round brilliant consists of 58 facets (or 57 if the culet is excluded), ordinarily today cut in two pyramids placed base to base: 33 on the ''crown'' (the top half above the middle or ''girdle'' of the stone), truncated comparatively near its base by the table, and 25 on the ''pavilion'' (the lower half below the girdle), which has only the apex cut off to form the culet, around which 8 extra facets are sometimes added. In recent decades, most girdles are faceted. Many girdles have 32, 64, 80, or 96 facets; these facets are not counted in the total. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not universally agreed upon. One may speak of the ''American cut'' or the ''Scandinavian standard'' (''Scan. D.N.''), to give but two examples. Today, Tolkowsky's "ideal" model has been overused. The original model was a general guideline, as there were several aspects of diamond-cutting that were not explored or accounted for in that model. Figures 1 and 2 show the facets of a round brilliant diamond. Figure 1 assumes that the "thick part of the girdle" is the same thickness at all 16 "thick parts". It does not consider the effects of indexed upper girdle facets. Figure 2 is adapted from Figure 37 of Marcel Tolkowsky's Diamond Design,〔http://www.folds.net/diamond_design/index.html#fig_37〕 which was originally published in 1919. Since 1919, the lower girdle facets have become longer. As a result, the pavilion main facets have become narrower. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Brilliant (diamond cut)」の詳細全文を読む スポンサード リンク
|